The present invention relates to a migration measuring method and measuring apparatus. More particularly, the present invention relates to a migration measuring method and measuring apparatus for evaluating the resistance to insulation deterioration of materials and components of electronic equipment due to migration.
It is conventionally well known that when an electric field is applied onto a conductor circuit board with water sticking thereto, elution and deposition of electrode material are repeated, soon causing generation of short circuit between electrodes, that is, so-called ionic migration or electrochemical migration (hereinafter called migration) takes place. It is known that such migration is more liable to take place when the space between electrodes is narrower and is especially liable to take place in silver, copper and solder.
Accordingly, with a recent trend of circuits becoming higher in density and finer in pitch due to reduction in size and weight of electronic equipment, the influence of migration on the insulation deterioration of electronic equipment is increasingly becoming a matter of importance, and for the improvement of reliability of electronic equipment, it is now an urgent problem to make clear the basic reaction mechanism of migration and to enable the evaluation thereof.
And, a conventional migration measuring method for evaluating the migration resistance of various materials is generally such that generation of migration is observed by aiming at electrical characteristics such as change in insulation resistance due to short circuit between electrodes (for example, refer to Japanese Laid-open Patent H11-211684).
However, such conventional migration measuring method is substantially a follow-up analysis, which is not the analysis of the generation process of migration that is electro-chemical phenomenon. Also, the period of measurement is very long (for example, 1,000xcx9c2,000 hours), and as a result, it causes hindrance to the purpose of shortening the product evaluation period that occupies a large portion of the period for product development.
In order to solve the problem, the inventor et al have already proposed a migration measuring method and measuring apparatus which enable the prediction of generation of migration by applying a QCM (Quartz Crystal Microbalance) method to the measurement of migration so that the process of migration can be measured in real time [Refer to November 2000: the Reliability engineering association of Japan, the 13th Reliability Symposium Announcement Reports (p27xcx9cp30), Patent Application No. 2001-095913].
FIG. 16 shows the measuring principles of the migration measuring method and measuring apparatus previously proposed by the inventor et al. In the measuring apparatus 100, an electrode (working electrode) 102 formed on the surface of crystal plate 101 and a bar electrode (counter electrode) 103 with metal-plated layer (e.g. solder-plated layer) formed thereon are arranged opposing to each other via insulating material 104 being high in hygroscopicity such as filter paper, and with ion-exchanged water 105 dripped into the gap between the electrodes 102 and 103, a predetermined DC voltage is applied thereto, then the change in the number of vibrations of the crystal plate 101 is measured, thus detecting the alteration in mass of the working electrode 102, and thereby, the quantity of metal ion deposited on the working electrode 102 is measured in real time.
However, the actual generation process of migration includes a number of elementary steps (such as charge transfer and mass transfer), and measuring the change in mass between electrodes by the QCM method is not enough to obtain the information in these elementary steps and to sufficiently make clear the generation mechanism of migration. Accordingly, it is often unable to precisely predict the period of generation of short circuit between electrodes and to achieve sufficient reliability. As a result, there arises a problem that the evaluation period cannot be effectively shortened.
The present invention is intended to solve the problems of the migration measuring method and measuring apparatus related to the proposal previously made by the inventor et al, and the main object of the invention is to provide a migration measuring method and measuring apparatus which enable more precise prediction of the generation mechanism of migration so that the generation period of migration can be more precisely predicted, and the invention is also intended to provide a short-circuit generation time predicting method and short-circuit generation time predicting apparatus for predicting short circuit between electrodes due to migration by using the data obtained by the measurement.
The first aspect of the migration measuring method of the present invention is a migration measuring method based on an alternating current impedance method, wherein direct current with fine alternating current superposed is applied across electrodes to measure impedance therebetween, and then surface static capacity is calculated from the measured value of impedance in order to measure migration in accordance with the variation of the calculated static capacity.
In the first aspect of the migration measuring method of the present invention, generation of migration is detected by detecting rapid decrease of surface static capacity after lapse of a given time since the start of impedance measurement.
The second aspect of the migration measuring method of the present invention is a migration measuring method based on an alternating current impedance method, wherein direct current with fine alternating current superposed is applied across electrodes to measure the impedance therebetween, and then charge transfer resistance is calculated from the measured value of impedance in order to measure migration in accordance with the variation of the calculated charge transfer resistance.
In the second aspect of the migration measuring method of the present invention, generation of migration is detected by detecting rapid decrease of charge transfer resistance after lapse of a given time since the start of impedance measurement.
The third aspect of the migration measuring method of the present invention is a migration measuring method based on an alternating current impedance method, wherein direct current with fine alternating current superposed is applied across electrodes to measure the impedance, and then surface static capacity and charge transfer resistance are calculated from the measured value of impedance in order to measure migration in accordance with the variation of the calculated surface static capacity and charge transfer resistance.
In the third aspect of the migration measuring method of the present invention, generation of migration is detected by detecting rapid decrease of surface static capacity and charge transfer resistance after lapse of a given time since the start of impedance measurement.
The short-circuit generation time predicting method of the present invention is a short-circuit generation time predicting method based on an alternating current impedance method for predicting the generation time of short circuit between electrodes due to migration, wherein direct current with fine alternating current superposed is applied across electrodes to measure the impedance therebetween, and then charge transfer resistance is calculated from the measured value of impedance in order to measure the generation time of short circuit due to migration in accordance with the calculated charge transfer resistance.
In the short-circuit generation time predicting method of the present invention, the short-circuit generation predicted time is calculated by the following equation when a water drop method is applied.
TE=TD+(RctB/(RctBxe2x88x92RctD))0.5xc3x97TS
where
TE: short circuit generation predicted time
TD: time until inflection point detection
RctB: charge transfer resistance before inflection point detection
RctD: charge transfer resistance at inflection point detection
TS: measuring time interval
Also, in the short-circuit generation time predicting method of the present invention, the short-circuit generation predicted time is calculated by the following equation when an environmental test method or humidity test method is applied.
TE=TD+(Rcte/(Rctexe2x88x92Rctd))0.5xc3x97((Rcte+Rsol)/Rcte)2xc3x97TS
where
TE: short circuit generation predicted time
TD: time until inflection point detection
Rcte: charge transfer resistance before inflection point detection (charge transfer resistance during stable period)
Rctd: charge transfer resistance at inflection point detection
Rsol: resistance before inflection point detection
TS: measuring time interval
Thus, in the method of the present invention, for example, an anode is a bar-shaped electrode, and a cathode is a flat-plate electrode.
The first aspect of the migration measuring apparatus of the present invention is a migration measuring apparatus based on an alternating current impedance method, comprising a superposed signal applying section for applying direct current with fine alternating current superposed across electrodes; a current measuring section; an impedance measuring section for measuring impedance between electrodes; and a measured data recording and processing section for recording the value measured by the impedance measuring section in order to measure the migration, wherein the measured data recording and processing section calculates surface static capacity from the measured value of impedance and measures the migration in accordance with the variation of the calculated surface static capacity.
In the first aspect of the migration measuring apparatus of the present invention, the generation of migration is detected by detecting rapid decrease of surface static capacity after lapse of a given time since the start of the impedance measurement.
The second aspect of the migration measuring apparatus of the present invention is a migration measuring apparatus using an alternating current impedance method, comprising a superposed signal applying section for applying direct current with fine alternating current superposed across electrodes; a current measuring section; an impedance measuring section for measuring impedance between electrodes; and a measured data recording and processing section for recording and processing the value measured by the impedance measuring section in order to measure the migration, wherein the measured data recording and processing section calculates charge transfer resistance from the measured value of impedance and detects the generation of migration in accordance with the variation of the calculated charge transfer resistance.
In the second aspect of the migration measuring apparatus of the present invention, the measured data recording and processing section detects the generation of migration by detecting rapid decrease of charge transfer resistance after lapse of a given time since the start of the impedance measurement.
The third aspect of the migration measuring apparatus of the present invention is a migration measuring apparatus using an alternating current impedance method, comprising a superposed signal applying section for applying direct current with fine alternating current superposed across electrodes; a current measuring section; an impedance measuring section for measuring impedance between electrodes; and a measured data recording and processing section for recording and processing the value measured by the impedance measuring section in order to measure the migration, wherein the measured data recording and processing section calculates surface static capacity and charge transfer resistance from the measured value of impedance and measures the migration in accordance with the variation of the calculated surface static capacity and charge transfer resistance.
In the third aspect of the migration measuring apparatus of the present invention, the generation of migration is detected by detecting rapid decrease of surface static capacity and charge transfer resistance after lapse of a given time since the start of impedance measurement.
The short-circuit generation time predicting apparatus of the present invention is a short-circuit generation time predicting apparatus using an alternating current impedance method for predicting the generation time of short circuit between electrodes due to migration, comprising a superposed signal applying section for applying direct current with fine alternating current superposed across electrodes, a current measuring section, an impedance measuring section for measuring impedance between electrodes, and a measured data recording and predicting section for recording the value measured by said impedance measuring section and predicting the generation time of short-circuit between electrodes due to migration, wherein charge transfer resistance is calculated from the measured value of impedance, and the generation time of short circuit due to migration is predicted in accordance with the calculated charge transfer resistance.
In the short-circuit generation time predicting apparatus of the present invention, short-circuit generation predicted time is calculated by the following equation when a water drop method is applied.
TE=TD+(RctB/(RctBxe2x88x92RctD))0 5xc3x97TS
where
TE: short-circuit generation predicted time
TD: time until inflection point detection
RctB: charge transfer resistance before inflection point detection
RctD: charge transfer resistance at inflection point detection
TS: measuring time interval
Also, in the short-circuit generation time predicting apparatus of the present invention, the short-circuit generation predicted time is calculated by the following equation when an environmental test method or humidity test method is applied.
TE=TD+(Rcte/(Rctexe2x88x92Rctd))0.5xc3x97((Rcte+Rsol)/Rcte)2xc3x97TS
where
TF: short-circuit generation predicted time
TD: time until inflection point detection
Rcte: charge transfer resistance before inflection point detection (charge transfer resistance during stable period)
Rctd: charge transfer resistance at inflection point detection
Rsol: solution resistance before inflection point detection
TS: measuring time interval
In the apparatus of the present invention, for example, an anode is a bar-shaped electrode, and a cathode is a flat-plate electrode.
Since the present invention has a configuration as described above, it is possible to accurately measure the process of migration in real time or on-line.
Also, according to the preferred embodiment of the present invention, short circuit between electrodes due to migration can be predicted, and it is possible to shorten the time required for the evaluation of migration resistance and to improve the productivity.